Retroviremia in Commercial Pigs and Its Preliminary Association with Poor Health

Autor: Meritxell Donadeu, Martha M. Mellencamp, Linda Scobie, Alexander W. Tucker
Rok vydání: 2006
Předmět:
Zdroj: Journal of Clinical Microbiology. 44:3846-3847
ISSN: 1098-660X
0095-1137
DOI: 10.1128/jcm.01378-06
Popis: We report the novel discovery of age-related titers of circulating retroviral elements in pig serum and a preliminary association with background disease status. Exogenous retroviruses have previously not been described for pigs; however, porcine endogenous retroviruses (PERV) are well characterized due to their potential significance and the risks associated with microbiological safety in clinical xenotransplantation. Three subtypes of PERV have been identified in the pig genome. PERV A and B are present in the genomes of all pigs, and immortalized pig cell lines were able to produce virus capable of infection of certain pig and human cell lines (8). In contrast, PERV C is absent from many pigs and this virus is not infectious to human cells. More recently, the possible existence of exogenous (and therefore transmissible) as opposed to endogenous retroviruses (ERV) in pigs was proposed by Scobie et al. (6, 9). They described a PERV A/PERV C recombinant retrovirus released from mitogen-stimulated porcine peripheral blood mononuclear cells that was not present in a proviral form in the pig genome. ERVs account for around 5% of the vertebrate genome (3) and represent previously exogenous retroviruses that have integrated into the host germ line with evolutionary, physiological, and pathological consequences (5). Human ERV have been associated with neoplasia, congenital defects, and autoimmune diseases (4), and retrovirus-like particles have been described for human fetal serum (2) and synovial fluid from cases of rheumatoid arthritis (7). To date, few studies have investigated a causal relationship between ERV and disease and there is no evidence for retrovirus-associated pathogenesis in pigs. Further, ERV expression has been considered a marker of disease, through secondary activation, rather than a causal agent (4). However, in mice, an immune complex-mediated nephritis has been causally associated with ERV (1). Therefore, in pigs, retroviremia (endogenous, exogenous, or both) might be associated with increased susceptibility to disease, either through directly pathogenic effects or through immune dysfunction. The current study investigated the prevalence and quantity of viral RNA in serum as an indicator of retroviremia in commercial pigs. The study used a real-time reverse transcriptase PCR (RT-PCR) approach, with primers (kindly supplied by Prof. D. Onions, Q-One Biotech Ltd., Glasgow, Scotland) directed at a pol gene sequence conserved across all currently known PERV A, B, and C types, to analyze viral RNA extracted from 87 pig sera. The sera originated from four farms: farm 1, a specific pathogen-free colony of Danish Ellegaard minipigs (free from porcine reproductive and respiratory syndrome virus [PRRSV] and postweaning multisystemic wasting syndrome [PMWS]); farm 2, a United Kingdom Large White cross herd (free from PRRSV and PMWS); farm 3, a United Kingdom Large White cross herd, positive for PRRSV and PMWS; and farm 4, a Spanish Large White cross herd, negative for PRRSV and PMWS. The results (Fig. ​(Fig.1a)1a) show that serum-associated PERV RNA was detected in all but one (86/87) of the serum samples (range, 0 to 5.74 × 106 copies/ml serum). A univariate analysis of variance (ANOVA; SPSS 13.0), performed with PERV RNA serum titer (as a response variable) measured on the log scale in order to meet ANOVA assumptions, and farm and age as response variables indicated significant differences in PERV RNA serum titer in consideration of farm (P < 0.0001) and age of pig sampled (P < 0.0001). There was also strong evidence of an interaction between farm and age (P = 0.057), although this is not quite significant at the 5% level. FIG. 1. (a) Box whisker plots of PERV RNA detection in pig serum samples (RNA copies/ml serum) collected from pigs of defined age groups on four different farms (a total of 87 pigs across four farms). On farm 1 (Danish minipigs, high health), 6 pigs >6 ... Overall, there was a tendency for increased levels of serum viral RNA in pigs aged 20% for farm 3, ∼10% for farm 4, and
Databáze: OpenAIRE
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